Background that particles sit in

What is the nature of the background that particles sit in ? Everyone says its space-time, but then its non local and all kinds of strange things seem to happen.

Even if we say they are fields and not particles (or even both), why is it that people think that particles sit in spacetime when they show characteristics that are clearly different from what normally happens in spacetime ?

Why do the theortical physicists look for a way to make particles appear in a background independant way such that particles will create the background, when we have no reason to believe that particles are not just a misunderstanding of energy resonating in a layer of reality we call spacetime ?

Is the background really spacetime ? If so, what evidence is there for that?

Particles sitting on spacetime seems up for challenge. Einsteins General theory suggests that particles are in fact part of the vacuum, making the vacuum a physical sheet. The background of spacetime is the zero-point energy field, a density energy making up all available energy in the universe.

I don't really understand "density energy". But if we take both spacetime and particles as being phenomena emerging from this "zero point vacuum" background, surely a Theory of Everything should describe the background rather than trying to create it out of what emerges from it ?

Or does anyone believe that our concept of 4D spacetime is the geometric totality on which a TOE will sit ?